I'm wondering the same thing. I grabbed the Astral Media plugin from svn, putting it in /usr/share/xbmc/addons/plugin.video.astral.media/
Even after restarting XBMC, it does not appear in the addons list nor in the video plugins list (which is empty). I am using XBMC build 30704.

I've managed to "hack" in a couple skins by creating the necessary addon.xml file and I'm trying to do the same for a couple video plugins. I've read that it's possible. What am I doing wrong?

Where the progwindow.GUI(config.appSkin ,config.rootDir, config.skinFolder) is the WindowXML class. The first parameter is the XML file for the skin. The second on the rootdir of the script and the last one the skin name.